"CanPlaceOn" tag not working via /summon

When using /summon, tags like CanPlaceOn are ignored, which means that
/summon Item ~ ~ ~ {Item:

{id:1,Damage:2,Count:1}

,PickupDelay:0,CanPlaceOn:["redstone_block"]}
won't work, but
/give GrmpfhcGames stone 1 2

{PickupDelay:0,CanPlaceOn:["redstone_block"]}

will.